1. Technical Field
The present invention relates to a beam and in particular to a beam for absorbing impact forces imparted to doors and sides of a car body as a result of collisions from the side as well as from the front and rear of the car. The beam is intended to protect people inside the car against personal injury in the case of such an impact.
2. Description of the Background Art
The need for special side impact protection for motorcar doors arose in the early 1970's after a decision from the U.S. National Highway Traffic Safety Administration (NHTSA) required all cars sold in the USA to have side doors that provide protection against intrusion, “Static Door Intrusion—FMVSS 214”. The European Union has since adopted corresponding requirements. Additional requirements have also been implemented by car manufacturers to provide impact absorption areas in door structures for various kinds of front and rear-end collisions.
The automotive industries efforts regarding environmental aspects have mainly focused on efficient emission control and reduced emission levels. Stricter emission control regulations and increased fuel prices are a driving force behind reducing fuel consumption in motorcars. This is being achieved by the construction of engines with improved fuel economy and lower emission levels, and new design solutions which make cars lighter. In practice, this involves using new design solutions and lighter body components. Lighter components, however, must not impair collision safety and newly developed body designs must instead be lighter and stronger than they have been up to the present day.
A number of patent and patent application specifications disclosed in the prior art disclose a number of beams for these and other purposes and are briefly described below. International Publication No. WO 00/17464A discloses a thick-walled beam section, “Floor beam”, with wide longitudinal channels and a bottom flange intended to support prefabricated building elements cast in concrete for the construction industry. U.S. Pat. No. 5,540,016 “Structural Beam” describes a door reinforcement member for vehicles formed by extruding aluminium alloy with varying material thickness along its length on two sides. The purpose of the member is to obtain optimum strength and energy absorption in relation to its weight. International Publication No. WO 00/35610“Structural member” describes a structural beam for e.g. vehicle bumper rails of extruded aluminium alloy with double hollow sections of variable height along its length with the purpose of obtaining optimum strength and energy absorption in relation to its weight.
The main objective of the present invention is to achieve a new and lighter beam element that also offers a flexible use of the basic beam structure having a minimum cross-section and a standarized profile. The advantages of such a beam are that it is compact and a complete solution is obtainable from the drawing board. There are also low product development costs, a short design time, low test-specimen costs and low production tool costs.
Accordingly, the present invention provides a beam for absorbing impact farces characterized in that the beam is provided by at least one thin walled, closed profile roll formed member defining a cavity wherein at least one wall of the member defines at least one longitudinally extending groove.
Preferably, the beam comprises more than one member and adjacent members are connected by an integrally formed web section.
Ideally, any wall of the member defining a groove is orientated substantially perpendicular to the direction of impact forces.
Ideally, the beam is formed from a steel material having a relatively low yield point in the unhardened state. The material from which the beam is formed has a low yield point of approximately 340 MPa but the yield point of the formed beam is extremely high due to the manufacturing and hardening process, approximately 1100 MPa. The beam has no special type of flanges and thereby obtains a low-weight beam structure.
In material with a high stress/strain relationship, buckling phenomena can often be a limiting factor and can lead to the beam section collapsing. In order to increase the efficiency of the section's modulus of rigidity/capacity and to provide impact protection with the desired absorption of collision energy during deformation by retaining a high modulus of rigidity in the case of deep intrusion, the beam is provided with one or more longitudinal grooves extending inwardly towards or outwardly from the center of the beam.
Preferably, the dimensions of the longitudinal grooves are dependent upon both the wall thickness and the lateral length of the wall of the beam in which the longitudinal groove is housed. As the lateral length of the beam increases, it is necessary to increase the depth of the groove in order to maintain the optimal efficiency of the beams modulus of rigidity/capacity.
Preferably, the dimensions of a groove for a normal wall thickness in the range of 0.7–1.0 mm are 3 mm in depth, 3 mm in width and with a small corner radius.
Preferably, the corners of the beam are provided with corner radii which are small relative to the material thickness of the beam, when the beam is non-cylindrical. The small radii are achievable as the material has a low tensile strength during the roll forming process prior to the heat-treating process. The corner radii are small in comparison with corner radii which may be formed when using materials with a high tensile strength and the same or similar material thickness.
Preferably, the steel is a steel alloy sheet.
Ideally, the steel is boron steel.
In a preferred embodiment, pre-coated steel having a corrosion protective coat is used. The use of this type of pre-coated steel removes the need for expensive coating processes after forming.
In a particularly preferred embodiment, the coating material is USIBOR 1500 PRE-COATED.
Preferably, the thin-walled hollow beam has a normal material thickness in the range of 0.7–1.8 mm.
Ideally, a seam weld extending between the longitudinal edges of the member closes the beam. The seam weld extends along the entire longitudinal length of the beam.
Preferably, a seam weld extending between the longitudinal edges of each member and the integrally formed web section closes the beam.
Ideally, the material throughout the closed profile beam including the seam weld has a yield point of at least 1100 MPa. The yield point of the steel combined with the efficient design is distinguished from corresponding known designs of side impact protection. Such designs include circular steel tube sections, high-alloy aluminium sections with yield point of approximately 360 MPa, cold-pressed open beams of high-tensile steel and open beams of hardened boron steel produced through hot pressing.
Ideally, at least one wall of the member defines laterally extending stiffening grooves.
Preferably, the laterally extending stiffening grooves project mainly inwardly from a wall of the member and are equispaced from one another along the wall of the member.
In a further aspect of the invention, the yield point of the material used on any predetermined longitudinal sections of the beam is on a lower level approximately 340 MPa when compared with the yield point of at least 1100 MPa for the rest of the beam.
Preferably, a section of the beam with a lower yield point is located adjacent the normal sitting position of a car seat occupant. The section of the beam striking the occupant during a side impact collision will be more susceptible to deformation thereby reducing the injuries caused to the occupant by the beam as a result of an intrusion.
In another aspect of the invention, the beams are formed for inter-engagement with one another by means of correspondingly located mating parts wherein a number of beams may be assembled together to build a wall element.
Preferably, each beam is provided wit a male part and a female part for mating with adjacent beams. This arrangement is particularly useful for use in the side, front and rear walls of transport vehicles such as articulated trucks. The wall elements built from the beams absorb impacts from heavy articles inside the container which may have come loose during transportation or absorb impacts as a result of external collisions wit other objects or vehicles. The beams may also be used in the building industry to assemble structural elements having similar strength requirements.
The present invention also provides an impact protection assembly comprising at least an outer beam mounted on a door between door ends wherein the beam is provided by at least one thin walled, closed profile roll formed member defining a cavity wherein at least one wall of the member defines at least one longitudinally extending groove.
Preferably, the impact protection assembly comprises an outer beam and an upper beam, the outer beam being mounted between the door ends and the upper beam being mounted on the inner door panel between the door ends. The upper beam takes a substantial portion of the impact load during a front or rear collision which reduces the risk of a door buckling inwards or outwards during a collision. This helps to maintain the compartment space afforded to a vehicle occupant during a collision.
Ideally, the upper beam comprises two members connected by a web section and the outer beam comprises a single member.
Preferably, both of the members of the upper beam are provided with a single longitudinally extending groove on one corresponding wall of each member and the single member of the outer beam defines two grooves on two opposite walls of the member and laterally extending stiffening grooves on at least one other wall.
Ideally, when a car is provided with only two doors, the beams are welded onto the coachworks of the car where rear door side impact protection would normally be located in order to provide protection for passengers in the rear of the vehicle.
The present invention also provides a method of manufacturing a beam for absorbing impact forces wherein at least one thin walled, closed profile member is roll formed with at least one longitudinally extending groove on at least one wall of the member while the sheet material is still in its unhardened state.
Advantageously, the method gives high material utilization. A low total amount of steel material is required in the roll forming process of a comparatively thin profile clement. This gives an extremely high material utilization which offers a favorable environmental impact (environment factor) during manufacture compared with the environmental impact from other existing designs of side impact protection in doors. This quality is nowadays an important factor within the automotive industry when selecting materials and designs for a function/component. The entire vehicle is considered and environmentally calculated with an environment declaration for the individual functions/components.
Preferably, the method includes the step of roll forming lateral stiffening grooves into at least one wall of the member.
Ideally, the method also provides for the rolling of corner radii which are small relative to the material thickness into one or more of the corners of the beam.
Preferably, the method of manufacturing the beam also includes the steps of joining a seam with a continuous weld; passing the beam through induction coils; heating to a hardening temperature; cooling by spraying water directly onto the beam and finally cutting the beam to the necessary length.
Ideally, the method of manufacturing the beam includes the step of applying a tension to the leading edge of the beam to improve the straightness of the beam. The tension is applied to the beam by running the rollers at the end of the production line at a slightly increased speed relative to the other rollers. This maintains a constant tensile force on the beam as it passes through the production apparatus.
Preferably, the rollers at the end of the production line are positioned in order to form the beam by bending over the entire length of the beam. The desirable radius of curvature applied to the beam is extremely large and typically although not exclusively) for a beam having a length of 1 meter there is an approximate displacement of 10 mm from the straight position for the midpoint of the beam after forming.
Ideally, the hardening temperature is approximately 920° C.
Preferably, the beam is welded in its hardened state to attachment brackets or directly to adjacent structural members.
Preferably, the method includes the step of local heating of predetermined longitudinal sections of the beam by means of inductive heating to tempering temperature with subsequent cooling in order to produce a beam having independent yield strength values for individual longitudinal sections of the beam. In this way, the risk of personal injury to hips/shoulders can be reduced as predetermined longitudinal sections of such a beam deform more readily due to their reduced yield strength value.